Sources of infection & Treatment of Tuberculosis

The most common source of Tuberculosis infection is the human case whose sputum is positive for the tubercle bacilli, and who has either received no treatment for it or not got treated fully. Such sources can discharge the bacilli in their sputum for years.

Bovine source
The bovine source of infection is usually infected milk. There is no definite evidence that bovine tuberculosis is a problem in this country because of the practice of boiling milk before consumption.

Treatment of tuberculosis
Tuberculosis is a curable disease. Many drugs are available for the treatment of tuberculosis. There are now 12 or 13 drugs available for the treatment of tuberculosis. Some drugs are bactericidal (i.e. they kill the bacteria) and some of the drugs are bacteriostatic (i.e. they do not kill but prevent them from dividing and arrest their growth). The drugs are always used in combination to enhance the effectiveness of therapy and prevent the development of resistance.

Bactericidal Drugs for TuberculosisRifampicin
RMP is used only as an oral drug. The total daily dose (10 to 12 mg/kg body weight) should be taken at least an hour before or about two hours after food because absorption is reduced by food. It is never used alone for the treatment of tuberculosis, but always used in combination with INH or another drug.

Side effects
Many patients develop nausea at the start of treatment, but this passes off. The more dangerous side–effects is to the liver (hepatitis) which may necessitate stopping the drug altogether.

Warning to the patient
The patient should be told that the drug will turn the urine red, this can be used as test of compliance. If Rifampicin is stopped for some reason, it should not be restarted within three weeks to avoid hypersensitivity.

INH
INH is a very effective drug in the treatment of tuberculosis. INH should be given as a single daily dose (4 to 5 mg/kg of body weight, subject to a maximum dose of 300 mg).

Precaution
Vitamin B6 (10 to 20 mg daily) should be prescribed along with this medicine to prevent its toxic effects on the nerves.

Streptomycin
The daily dose of streptomycin is 0.75 to 1g in a single injection.

Side effects
It can cause side–effects which include damage to the inner structures of the ear and to the kidneys. Dose adjustment is required in those with renal failure.

Pyrazinamide
It is particularly active against slow–multiplying organisms which reside within the cells, and which are unaffected by other drugs. The drug is given orally and the usual dose in 30 mg/kg of body weight (an average of 1.5 to 2g) divided into two or three doses per day, or 45 to 50 mg/kg body weight (average 2 to 3 g) twice weekly.
Complications include injury to the liver and the propensity to cause high uric acid levels. Pyrazinamide is a good drug to use when the nervous system is affected by tuberculosis, particularly meningitis.

Bacteriostatic Drugs for TuberculosisEthambutol
Ethambutol is used in combination to prevent the emergence of resistance to other drugs. It is given orally. Its major side–effect is to the eye to cause neuritis. There are other bacteriostatic drugs such as ethionamide, prothimide, PAS, cycloserine, kanamycin, viomycin and capreomycin.

Two Phase ChemotherapyThere are two phases in the effective treatment of tuberculosis:

The first is a short, aggressive or intense phase, early in the course of treatment, lasting 1 to 3 months. During this intensive phase, three or more drugs are combined to kill as many bacilli as possible. The more rapidly the bacilli are killed initially, the less likely are persisters to emerge. The risk of relapse is also lessened.

The second or the continuation phase is aimed at sterilizing the smaller number of dormant or persisting bacilli.

Short Course Chemotherapy
There are now a number of short course regimens of six months’ duration that are highly effective, of low toxicity and well tolerated. These potent regimens are based on an initial intensive phase with four drugs in the continuation phase, (INH plus rifampicin or thioacetazone) given daily or intermittently. The treatment must be fully supervised and monitored mainly by bacteriological examination.

Tuberculosis

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